Procedure: Isolations Under the Permit to Work System

Purpose. This procedure describes the steps to plan, prove, tag, record and restore an isolation of a gas asset under a permit to work.

1.Scope

This procedure applies to every isolation of a main, service, regulator, valve or facility on the network for construction, maintenance or emergency work. It must be read with the Permit to Work and Isolation Policy.

2.Step 1: Plan the isolation

The permit issuer must identify the isolation points on the network drawings and confirm them against the asset register. The issuer must estimate how many customers will lose supply and must notify the control centre before the permit is issued. Where more than 50 customers are affected, the Construction Manager or Maintenance and Integrity Manager must approve the outage.

3.Step 2: Prove the isolation

The permit holder must close and tag each isolation valve, then prove that the work face is isolated by reading pressure with a calibrated gauge or by confirming zero flow. A valve in the closed position is not proof of isolation. The proven reading must be written on the permit.

• Close and tag each valve or squeeze-off point
• Read pressure at the work face with a calibrated gauge
• Wait five minutes and read again
• Record both readings on the permit

4.Step 3: Purge and monitor

Before breaking into a pipe the holder must purge the isolated section to a safe atmosphere and must monitor continuously with a calibrated portable detector. Readings above 10 percent of the lower explosive limit inside the excavation must stop the work.

5.Step 4: Restore supply

Restoration must be requested from the control centre and must only begin when the control centre confirms. Air must be purged from the repaired section before customers are reconnected. Every affected customer must be relit by an authorised technician who tests the installation before leaving.

6.Step 5: Record and close

The permit holder must record the isolation points, readings, purge and restoration on the permit, then close the permit in the Permit to Work Register within 24 hours. The control centre must record the isolation and restoration times in the operations log.